Neurotensin (NT), a peptide localized in the central and peripheral nervous system and the gastrointestinal tract, is an important regulator of intestinal motility, secretion and blood flow. Current approaches for determining the regulation of NT release rely on in vivo determinations that cannot assess the site and mechanisms of secretagogue action on NT cells. The availability of two recently developed primary culture systems comprised of NT-containing mucosal endocrine cells and NT-containing submucosal neurons, respectively, provides an opportunity to investigate questions regarding NT release that were previously difficult to assess. The long term objectives of this project are to understand the regulation of NT release at the cell level and to define the intracellular mechanisms signalling peptide release. Neurotensin endocrine cell cultures will be used to 1) determine whether the cAMP-independent mechanism of somatostatin-inhibited NT release is coupled to dynamic changes in cell calcium and 2) characterize fatty acid-stimulated NT release with regard to stereospecificity and transduction of intracellular second messengers. Submocusal neuronal cultures will be used to 1) assess possible differences in transmitter regulation of NT- containing endocrine cells and nerve cells and 2) investigate whether Substance P-stimulated release of NT from neuronal cells is directly mediated by Substance P receptors on NT cells. The results of these studies will help define the nutrient and transmitter regulation of a single peptide expressed in both endocrine and neural cells, thus increasing current understanding of the coordinated actions of gastrointestinal hormones and transmitters in digestive function.